High-definition television (HDTV) provides a resolution that is substantially higher than that of standard-definition television.
HDTV may be transmitted in various varieties:
1080p - 1920×1080p: 2,073,600 pixels (approximately 2.1 megapixels) per frame
1080i - typically either:
1920×1080i: 1,036,800 pixels (approximately 1 megapixel) per field or 2,073,600 pixels (approximately 2.1 megapixels) per frame
1440×1080i:[1] 777,600 pixels (approximately 0.8 megapixels) per field or 1,555,200 pixels (approximately 1.6 megapixels) per frame
720p - 1280×720p: 921,600 pixels (approximately 0.9 megapixels) per frame
The letter "p" here stands for progressive scan while "i" indicates interlaced.
When transmitted at two megapixels per frame, HDTV provides about five times as many pixels as SD (standard-definition television).
History of high-definition television
Further information: Analog high-definition television system and History of television
The term high definition once described a series of television systems originating from the late 1930s; however, these systems were only high definition when compared to earlier systems that were based on mechanical systems with as few as 30 lines of resolution.
The British high-definition TV service started trials in August 1936 and a regular service on 2 November 1936 using both the (mechanical) Baird 240 line and (electronic) Marconi-EMI 405 line (377i) systems. The Baird system was discontinued in February 1937.[2] In 1938 France followed with their own 441-line system, variants of which were also used by a number of other countries. The US NTSC system joined in 1941. In 1949 France introduced an even higher-resolution standard at 819 lines (768i), a system that would be high definition even by today's standards, but it was monochrome only. All of these systems used interlacing and a 4:3 aspect ratio except the 240-line system which was progressive (actually described at the time by the technically correct term "sequential") and the 405-line system which started as 5:4 and later changed to 4:3. The 405-line system adopted the (at that time) revolutionary idea of interlaced scanning to overcome the flicker problem of the 240-line with its 25 Hz frame rate. The 240-line system could have doubled its frame rate but this would have meant that the transmitted signal would have doubled in bandwidth, an unacceptable option.
Colour broadcasts started at similarly higher resolutions, first with the US NTSC color system in 1953, which was compatible with the earlier B&W systems and therefore had the same 525 lines (480i) of resolution. European standards did not follow until the 1960s, when the PAL and SECAM colour systems were added to the monochrome 625 line (576i) broadcasts.
Since the formal adoption of digital video broadcasting's (DVB) widescreen HDTV transmission modes in the early 2000s the 525-line NTSC (and PAL-M) systems as well as the European 625-line PAL and SECAM systems are now regarded as standard definition television systems. In Australia, the 625-line digital progressive system (with 576 active lines) is officially recognized as high-definition.[3]
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Analog systems
Main article: analog high-definition television system
Early HDTV broadcasting used analog technology, but today it is transmitted digitally and uses video compression.
In 1949, France started its transmissions with an 819 lines system (768i). It was monochrome only, it was used only on VHF for the first French TV channel, and it was discontinued in 1985.
In 1958, the Soviet Union developed Тransformator,[4] the first high-resolution (definition) television system capable of producing an image composed of 1,125 lines of resolution aimed at providing teleconferencing for military command. It was a research project and the system was never deployed in the military or broadcasting.[5]
In 1979, the Japanese state broadcaster NHK first developed consumer high-definition television with a 5:3 display aspect ratio.[6] The system, known as Hi-Vision or MUSE after its Multiple sub-Nyquist sampling encoding for encoding the signal, required about twice the bandwidth of the existing NTSC system but provided about four times the resolution (1080i/1125 lines). Satellite test broadcasts started in 1989, with regular testing starting in 1991 and regular broadcasting of BS-9ch commenced on 25 November 1994, which featured commercial and NHK programming.
In 1981, the MUSE system was demonstrated for the first time in the United States, using the same 5:3 aspect ratio as the Japanese system.[7] Upon visiting a demonstration of MUSE in Washington, US President Ronald Reagan was most impressed and officially declared it "a matter of national interest" to introduce HDTV to the USA.[8]
Several systems were proposed as the new standard for the US, including the Japanese MUSE system, but all were rejected by the FCC because of their higher bandwidth requirements. At this time, the number of television channels was growing rapidly and bandwidth was already a problem. A new standard had to be more efficient, needing less bandwidth for HDTV than the existing NTSC.
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Demise of analog HD systems
The limited standardization of analogue HDTV in the 1990s did not lead to global HDTV adoption as technical and economic reasons at the time did not permit HDTV to use bandwidths greater than normal television.
Early HDTV commercial experiments such as NHK's MUSE required over four times the bandwidth of a standard-definition broadcast—and HD-MAC was not much better. Despite efforts made to reduce analog HDTV to about 2× the bandwidth of SDTV these television formats were still distributable only by satellite.
In addition, recording and reproducing an HDTV signal was a significant technical challenge in the early years of HDTV (Sony HDVS). Japan remained the only country with successful public broadcasting analog HDTV, with seven broadcasters sharing a single channel.
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Rise of digital compression
Since 1972, International Telecommunication Union's radio telecommunications sector (ITU-R) has been working on creating a global recommendation for Analogue HDTV. These recommendations however did not fit in the broadcasting bands which could reach home users. The standardization of MPEG-1 in 1993 also led to the acceptance of recommendations ITU-R BT.709.[9] In anticipation of these standards the Digital Video Broadcasting (DVB) organisation was formed, an alliance of broadcasters, consumer electronics manufacturers and regulatory bodies. The DVB develops and agrees on specifications which are formally standardised by ETSI.[10]
DVB created first the standard for DVB-S digital satellite TV, DVB-C digital cable TV and DVB-T digital terrestrial TV. These broadcasting systems can be used for both SDTV and HDTV. In the US the Grand Alliance proposed ATSC as the new standard for SDTV and HDTV. Both ATSC and DVB were based on the MPEG-2 standard. The DVB-S2 standard is based on the newer and more efficient H.264/MPEG-4 AVC compression standards. Common for all DVB standards is the use of highly efficient modulation techniques for further reducing bandwidth, and foremost for reducing receiver-hardware and antenna requirements.
In 1983, the International Telecommunication Union's radio telecommunications sector (ITU-R) set up a working party (IWP11/6) with the aim of setting a single international HDTV standard. One of the thornier issues concerned a suitable frame/field refresh rate, the world already having split into two camps, 25/50 Hz and 30/60 Hz, related by reasons of picture stability to the frequency of their main electrical supplies.
The IWP11/6 working party considered many views and through the 1980s served to encourage development in a number of video digital processing areas, not least conversion between the two main frame/field rates using motion vectors, which led to further developments in other areas. While a comprehensive HDTV standard was not in the end established, agreement on the aspect ratio was achieved.
Initially the existing 5:3 aspect ratio had been the main candidate but, due to the influence of widescreen cinema, the aspect ratio 16:9 (1.78) eventually emerged as being a reasonable compromise between 5:3 (1.67) and the common 1.85 widescreen cinema format. (Bob Morris explained that the 16:9 ratio was chosen as being the geometric mean of 4:3, Academy ratio, and 2.4:1, the widest cinema format in common use, in order to minimize wasted screen space when displaying content with a variety of aspect ratios.[11])
An aspect ratio of 16:9 was duly agreed at the first meeting of the IWP11/6 working party at the BBC's Research and Development establishment in Kingswood Warren. The resulting ITU-R Recommendation ITU-R BT.709-2 ("Rec. 709") includes the 16:9 aspect ratio, a specified colorimetry, and the scan modes 1080i (1,080 actively interlaced lines of resolution) and 1080p (1,080 progressively scanned lines). The British Freeview HD trials used MBAFF, which contains both progressive and interlaced content in the same encoding.
It also includes the alternative 1440×1152 HDMAC scan format. (According to some reports, a mooted 750-line (720p) format (720 progressively scanned lines) was viewed by some at the ITU as an enhanced television format rather than a true HDTV format,[12] and so was not included, although 1920×1080i and 1280×720p systems for a range of frame and field rates were defined by several US SMPTE standards.)
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Inaugural HDTV broadcast in the United States
HDTV technology was introduced in the United States in the 1990s by the Digital HDTV Grand Alliance, a group of television, electronic equipment, communications companies consisting of AT&T Bell Labs, General Instrument, MIT, Philips, Sarnoff, Thomson, Zenith and the Massachusetts Institute of Technology. Field testing of HDTV at 199 sites in the United States was completed August 14, 1994.[13] The first public HDTV broadcast in the United States occurred on July 23, 1996 when the Raleigh, North Carolina television station WRAL-HD began broadcasting from the existing tower of WRAL-TV south-east of Raleigh, winning a race to be first with the HD Model Station in Washington, D.C., which began broadcasting July 31, 1996 with the callsign WHD-TV, based out of the facilities of NBC owned and operated station WRC-TV.[14][15][16] The American Advanced Television Systems Committee (ATSC) HDTV system had its public launch on October 29, 1998, during the live coverage of astronaut John Glenn's return mission to space on board the Space Shuttle Discovery.[17] The signal was transmitted coast-to-coast, and was seen by the public in science centers, and other public theaters specially equipped to receive and display the broadcast.[17][18]
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European HDTV broadcasts
The first HDTV transmissions in Europe, albeit not direct-to-home, begin in 1990, when the Italian broadcaster RAI and Japanese broadcaster NHK used the HD-MAC and MUSE HDTV technologies to broadcast the 1990 FIFA World Cup. The matches were shown in 8 cinemas in Italy and 2 in Spain. The connection with Spain was made via the Olympus satellite link from Rome to Barcelona and then with a fiber optic connection from Barcelona to Madrid. After some HDTV transmissions in Europe the standard was abandoned in the mid-1990s.
The first regular broadcasts started on January 1, 2004 when the Belgian company Euro1080 launched the HD1 channel with the traditional Vienna New Year's Concert. Test transmissions had been active since the IBC exhibition in September 2003, but the New Year's Day broadcast marked the official launch of the HD1 channel, and the official start of direct-to-home HDTV in Europe.[19]
Euro1080, a division of the Belgian TV services company Alfacam, broadcast HDTV channels to break the pan-European stalemate of "no HD broadcasts mean no HD TVs bought means no HD broadcasts ..." and kick-start HDTV interest in Europe.[20] The HD1 channel was initially free-to-air and mainly comprised sporting, dramatic, musical and other cultural events broadcast with a multi-lingual soundtrack on a rolling schedule of 4 or 5 hours per day.
These first European HDTV broadcasts used the 1080i format with MPEG-2 compression on a DVB-S signal from SES's Astra 1H satellite. Euro1080 transmissions later changed to MPEG-4/AVC compression on a DVB-S2 signal in line with subsequent broadcast channels in Europe.
The number of European HD channels and viewers has risen steadily since the first HDTV broadcasts, with SES's annual Satellite Monitor market survey for 2010 reporting more than 200 commercial channels broadcasting in HD from Astra satellites, 185 million HD-Ready TVs sold in Europe (£60 million in 2010 alone), and 20 million households (27% of all European digital satellite TV homes) watching HD satellite broadcasts (16 million via Astra satellites).[21]
In December 2009 the United Kingdom became the first European country to deploy high definition content on digital terrestrial television (branded as Freeview) using the new DVB-T2 transmission standard as specified in the Digital TV Group (DTG) D-book. The Freeview HD service currently contains 4 HD channels and is now rolling out region by region across the UK in accordance with the digital switchover process.
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Notation
HDTV broadcast systems are identified with three major parameters:
Frame size in pixels is defined as number of horizontal pixels × number of vertical pixels, for example 1280 × 720 or 1920 × 1080. Often the number of horizontal pixels is implied from context and is omitted, as in the case of 720p and 1080p.
Scanning system is identified with the letter p for progressive scanning or i for interlaced scanning.
Frame rate is identified as number of video frames per second. For interlaced systems an alternative form of specifying number of fields per second is often used.[citation needed]
If all three parameters are used, they are specified in the following form: [frame size][scanning system][frame or field rate] or [frame size]/[frame or field rate][scanning system].[citation needed] Often, frame size or frame rate can be dropped if its value is implied from context. In this case the remaining numeric parameter is specified first, followed by the scanning system.
For example, 1920×1080p25 identifies progressive scanning format with 25 frames per second, each frame being 1,920 pixels wide and 1,080 pixels high. The 1080i25 or 1080i50 notation identifies interlaced scanning format with 25 frames (50 fields) per second, each frame being 1,920 pixels wide and 1,080 pixels high.[citation needed] The 1080i30 or 1080i60 notation identifies interlaced scanning format with 30 frames (60 fields) per second, each frame being 1,920 pixels wide and 1,080 pixels high.[citation needed] The 720p60 notation identifies progressive scanning format with 60 frames per second, each frame being 720 pixels high; 1,280 pixels horizontally are implied.
50 Hz systems support three scanning rates: 25i, 25p and 50p. 60 Hz systems support a much wider set of frame rates: 23.976p, 24p, 29.97i/59.94i, 29.97p, 30p, 59.94p and 60p. In the days of standard definition television, the fractional rates were often rounded up to whole numbers, e.g. 23.976p was often called 24p, or 59.94i was often called 60i. 60 Hz high definition television supports both fractional and slightly different integer rates, therefore strict usage of notation is required to avoid ambiguity. Nevertheless, 29.97i/59.94i is almost universally called 60i, likewise 23.976p is called 24p.[citation needed]
For commercial naming of a product, the frame rate is often dropped and is implied from context (e.g., a 1080i television set). A frame rate can also be specified without a resolution. For example, 24p means 24 progressive scan frames per second, and 50i means 25 interlaced frames per second.[22]
There is no standard for HDTV colour support. Until recently the color of each pixel was regulated by three 8-bit color values, each representing the level of red, blue, and green which defined a pixel colour. Together the 24 total bits defining colour yielded just under 17 million possible pixel colors. Recently[when?] some manufacturers have produced systems that can employ 10 bits for each colour (30 bits total) which provides for a palette of 1 billion colors, saying that this provides a much richer picture, but there is no agreed way to specify that a piece of equipment supports this feature. Human vision can only discern approximately 1 million colours so an expanded colour palette is of questionable benefit to consumers.
Most HDTV systems support resolutions and frame rates defined either in the ATSC table 3, or in EBU specification. The most common are noted below.
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High-definition display resolutionsVideo format supported [image resolution] Native resolution [inherent resolution] (W×H) Pixels Aspect ratio (W:H) Description
Actual Advertised (Mpixel) Image Pixel
720p
1280×720 1024×768
XGA 786,432 0.8 4:3 1:1 Typically a PC resolution (XGA); also a native resolution on many entry-level plasma displays with non-square pixels.
1280×720 921,600 0.9 16:9 1:1 Standard HDTV resolution and a typical PC resolution (WXGA), frequently used by high-end video projectors; also used for 750-line video, as defined in SMPTE 296M, ATSC A/53, ITU-R BT.1543.
1366×768
WXGA 1,049,088 1.0 683:384
(approx. 16:9) 1:1 A typical PC resolution (WXGA); also used by many HD ready TV displays based on LCD technology.
1080p/i
1920×1080 1920×1080 2,073,600 2.1 16:9 1:1 Standard HDTV resolution, used by Full HD and HD ready 1080p TV displays such as high-end LCD, plasma and rear projection TVs, and a typical PC resolution (lower than WUXGA); also used for 1125-line video, as defined in SMPTE 274M, ATSC A/53, ITU-R BT.709;
Video format supported Screen resolution (W×H) Pixels Aspect ratio (W:H) Description
Actual Advertised (Mpixel) Image Pixel
720p
1280×720 1248×702
Clean Aperture 876,096 0.9 16:9 1:1 Used for 750-line video with faster artifact/overscan compensation, as defined in SMPTE 296M.
1080p
1920×1080 1888×1062
Clean aperture 2,005,056 2.0 16:9 1:1 Used for 1125-line video with faster artifact/overscan compensation, as defined in SMPTE 274M.
1080i
1920×1080 1440×1080
HDCAM/HDV 1,555,200 1.6 16:9 4:3 Used for anamorphic 1125-line video in the HDCAM and HDV formats introduced by Sony and defined (also as a luminance subsampling matrix) in SMPTE D11.
At a minimum, HDTV has twice the linear resolution of standard-definition television (SDTV), thus showing greater detail than either analog television or regular DVD. The technical standards for broadcasting HDTV also handle the 16:9 aspect ratio images without using letterboxing or anamorphic stretching, thus increasing the effective image resolution.
A very high resolution source may require more bandwidth than available in order to be transmitted without loss of fidelity. The lossy compression that is used in all digital HDTV storage and transmission systems will distort the received picture, when compared to the uncompressed source.
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Standard frame or field rates
ATSC table 3 defines the following frame rates for digital high-definition television.[23]
23.976 Hz (film-looking frame rate compatible with NTSC clock speed standards)
24 Hz (international film and ATSC high-definition material)
25 Hz (PAL, SECAM film, standard-definition, and high-definition material)
29.97 Hz (NTSC standard-definition material)
59.94 Hz (ATSC high-definition material)
60 Hz (ATSC high-definition material)
The optimum format for a broadcast depends upon the type of videographic recording medium used and the image's characteristics. For best fidelity to the source the transmitted field ratio, lines, and frame rate should match those of the source.
Although PAL, SECAM and NTSC frame rates technically apply only to standard definition television, not HD, with the roll out of HD, countries maintained the heritage of their former systems. HDTV in former PAL countries operates at a frame rate of 50 Hz and HDTV in former NTSC countries operates at 60 Hz.[24]
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Types of media
Standard 35mm photographic film used for cinema projection has a much higher image resolution than HDTV systems, and is exposed and projected at a rate of 24 frames per second (frame/s). To be shown on standard television, in PAL-system countries, cinema film is scanned at the TV rate of 25 frame/s, causing a speedup of 4.1 percent, which is generally considered acceptable. In NTSC-system countries, the TV scan rate of 30 frame/s would cause a perceptible speedup if the same were attempted, and the necessary correction is performed by a technique called 3:2 Pulldown: Over each successive pair of film frames, one is held for three video fields (1/20 of a second) and the next is held for two video fields (1/30 of a second), giving a total time for the two frames of 1/12 of a second and thus achieving the correct average film frame rate.
See also: Telecine
Non-cinematic HDTV video recordings intended for broadcast are typically recorded either in 720p or 1080i format as determined by the broadcaster. 720p is commonly used for Internet distribution of high-definition video, because most computer monitors operate in progressive-scan mode. 720p also imposes less strenuous storage and decoding requirements compared to both 1080i and 1080p. 1080p-24 frame/s and 1080i-30 frame/s is most often used on Blu-ray Disc; as of 2011, there is still no disc that can support full 1080p-60 frame/s.
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Contemporary systems
Main article: Large-screen television technology
Besides an HD-ready television set, other equipment may be needed to view HD television. In the US, cable-ready TV sets can display HD content without using an external box. They have a QAM tuner built-in and/or a card slot for inserting a CableCARD.[25]
High-definition image sources include terrestrial broadcast, direct broadcast satellite, digital cable, IPTV, Blu-ray video disc (BD), and internet downloads. Sony's PlayStation 3 has extensive HD compatibility because of the Blu-ray platform, so does Microsoft's Xbox 360 with the addition of Netflix streaming capabilities, and the Zune marketplace where users can rent or purchase digital HD content.[26] The HD capabilities of the consoles has influenced some developers to port games from past consoles onto the PS3 and 360, often with remastered graphics.
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Recording and compression
Main article: High-definition pre-recorded media and compression
HDTV can be recorded to D-VHS (Digital-VHS or Data-VHS), W-VHS (analog only), to an HDTV-capable digital video recorder (for example DirecTV's high-definition Digital video recorder, Sky HD's set-top box, Dish Network's VIP 622 or VIP 722 high-definition Digital video recorder receivers, or TiVo's Series 3 or HD recorders), or an HDTV-ready HTPC. Some cable boxes are capable of receiving or recording two or more broadcasts at a time in HDTV format, and HDTV programming, some included in the monthly cable service subscription price, some for an additional fee, can be played back with the cable company's on-demand feature.
The massive amount of data storage required to archive uncompressed streams meant that inexpensive uncompressed storage options were not available in the consumer market until recently. In 2008 the Hauppauge 1212 Personal Video Recorder was introduced. This device accepts HD content through component video inputs and stores the content in an uncompressed MPEG transport stream (.ts) file or Blu-ray format .m2ts file on the hard drive or DVD burner of a computer connected to the PVR through a USB 2.0 interface.
Realtime MPEG-2 compression of an uncompressed digital HDTV signal is prohibitively expensive for the consumer market at this time, but should become inexpensive within several years (although this is more relevant for consumer HD camcorders than recording HDTV). Analog tape recorders with bandwidth capable of recording analog HD signals such as W-VHS recorders are no longer produced for the consumer market and are both expensive and scarce in the secondary market.
In the United States, as part of the FCC's plug and play agreement, cable companies are required to provide customers who rent HD set-top boxes with a set-top box with "functional" FireWire (IEEE 1394) upon request. None of the direct broadcast satellite providers have offered this feature on any of their supported boxes, but some cable TV companies have. As of July 2004, boxes are not included in the FCC mandate. This content is protected by encryption known as 5C.[27] This encryption can prevent duplication of content or simply limit the number of copies permitted, thus effectively denying most if not all fair use of the content.
Sunday, May 27, 2012
Friday, May 18, 2012
The Watch History
A watch is a small timepiece, typically worn either on the wrist or attached on a chain and carried in a pocket; wristwatches, however, are the most common type of watch used today. Watches evolved in the 17th century from spring powered clocks, which appeared in the 15th century. The first watches were strictly mechanical. As technology progressed, the mechanisms used to measure time have, in some cases, been replaced by use of quartz vibrations or electromagnetic pulses and are called quartz movements.[1] The first digital electronic watch was developed in 1970.[2]
Before wristwatches became popular in the 1920s, most watches were pocket watches, which often had covers and were carried in a pocket and attached to a watch chain or watch fob.[3] In the early 1900s, the wristwatch, originally called a Wristlet, was reserved for women and considered more of a passing fad than a serious timepiece. Real gentlemen, who carried pocket watches, were actually quoted as saying they would "sooner wear a skirt as wear a wristwatch"[4]. This all changed in World War I when soldiers on the battlefield found using a pocket watch to be impractical, so they attached the pocket watch to their wrist by a cupped leather strap. It is also believed that Girard-Perregaux equipped the German Imperial Navy in a similar fashion as early as the 1880s, which were used while synchronizing naval attacks and firing artillery.[4]
Most inexpensive and medium-priced watches used mainly for timekeeping are electronic watches with quartz movements.[1] Expensive, collectible watches valued more for their workmanship and aesthetic appeal than for simple timekeeping, often have purely mechanical movements and are powered by springs, even though mechanical movements are less accurate than more affordable quartz movements. In addition to the time, modern watches often display the day, date, month and year, and electronic watches may have many other functions. Watches that provide additional time-related features such as timers, chronographs and alarm functions are not uncommon. Some modern designs even go as far as using GPS[5] technology or heart-rate monitoring[6] capabilities.
History
The earliest dated watch known, from 1530
Main article: History of watches
See also: History of timekeeping devices This section requires expansion.
Watches evolved from portable spring driven clocks, which first appeared in 15th century Europe. Watches weren't widely worn in pockets until the 17th century.
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Movement
Different kinds of movements move the hands differently as shown in this 2 second exposure. The left watch has a mechanical 1/6 s movement, the right one has a "1 s" quartz movement
A Russian mechanical watch movement
A movement in watchmaking is the mechanism that measures the passage of time and displays the current time (and possibly other information including date, month and day). Movements may be entirely mechanical, entirely electronic (potentially with no moving parts), or a blend of the two. Most watches intended mainly for timekeeping today have electronic movements, with mechanical hands on the watch face indicating the time.
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Mechanical movements
Main article: Mechanical watch
Compared to electronic movements, mechanical watches are less accurate, often with errors of seconds per day, and they are sensitive to position, temperature[7] and magnetism.[8] They are also costly to produce, require regular maintenance and adjustment, and are more prone to failure. Nevertheless, the craftsmanship of mechanical watches still attracts interest from part of the watch-buying public. Skeleton watches are designed to leave the mechanism visible for aesthetic purposes.
Mechanical movements use an escapement mechanism to control and limit the unwinding and winding parts of a spring, converting what would otherwise be a simple unwinding into a controlled and periodic energy release. Mechanical movements also use a balance wheel together with the balance spring (also known as a hairspring) to control motion of the gear system of the watch in a manner analogous to the pendulum of a pendulum clock. The tourbillon, an optional part for mechanical movements, is a rotating frame for the escapement, which is used to cancel out or reduce the effects of gravitational bias to the timekeeping. Due to the complexity of designing a tourbillon, they are very expensive, and only found in "prestige" watches.[1]
The pin-lever escapement (called the Roskopf movement after its inventor, Georges Frederic Roskopf), which is a cheaper version of the fully levered movement, was manufactured in huge quantities by many Swiss manufacturers as well as Timex, until it was replaced by quartz movements.[9][10][11]
Tuning-fork watches use a type of electromechanical movement. Introduced by Bulova in 1960, they use a tuning fork with a precise frequency (most often 360 hertz) to drive a mechanical watch. The task of converting electronically pulsed fork vibration into rotary movement is done via two tiny jeweled fingers, called pawls. Tuning-fork watches were rendered obsolete when electronic quartz watches were developed. Quartz watches were cheaper to produce and even more accurate.
Main article: Mainspring
Traditional mechanical watch movements use a spiral spring called a mainspring as a power source. In manual watches the spring must be rewound periodically by the user by turning the watch crown. Antique pocketwatches were wound by inserting a separate key into a hole in the back of the watch and turning it. Most modern watches are designed to run 40 hours on a winding and thus must be wound daily, but some run for several days and a few have 192-hour mainsprings and are wound weekly.
Main article: Automatic watch
Automatic watch: An eccentric weight, called a rotor, swings with the movement of the wearer's body and winds the spring
A self-winding or automatic watches is one that rewinds the mainspring of a mechanical movement by the natural motions of the wearer's body. The first self-winding mechanism was invented for pocketwatches in 1770 by Abraham-Louis Perrelet,[12] but the first "self-winding", or "automatic", wristwatch was the invention of a British watch repairer named John Harwood in 1923. This type of watch allows for constant winding without special action from the wearer; it works by an eccentric weight, called a winding rotor, which rotates with the movement of the wearer's wrist. The back-and-forth motion of the winding rotor couples to a ratchet to automatically wind the mainspring. Self-winding watches usually can also be wound manually so they can be kept running when not worn or if the wearer's wrist motions are inadequate to keep the watch wound.
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Electronic movements
See also: Electric watch
Electronic movements have few or no moving parts, as they use the piezoelectric effect in a tiny quartz crystal to provide a stable time base for a mostly electronic movement. The crystal forms a quartz oscillator which resonates at a specific and highly stable frequency, and which can be used to accurately pace a timekeeping mechanism. For this reason, electronic watches are often called quartz watches. Most quartz movements are primarily electronic but are geared to drive mechanical hands on the face of the watch in order to provide a traditional analog display of the time, which is still preferred by some consumers.
Prototype of a Quartz Wristwatch, CEH Switzerland, 1967
In 1959 Seiko gave an order to Epson (a daughter company of Seiko and the actual brain behind the quartz revolution) to start developing a quartz wristwatch. The project was codenamed 59A and by the 1964 Tokyo Summer Olympics, Seiko had a working prototype of a portable quartz watch which took part in time measurements throughout the event.
The first prototypes of an electronic quartz wristwatch (not just portable quartz watches as the Seiko timekeeping devices at the Tokyo Olympics in 1964) were made by the CEH research laboratory in Neuchâtel, Switzerland. From 1965 through 1967 pioneering development work was done on a miniaturized 8192 Hz quartz oscillator, a thermo-compensation module and an inhouse-made, dedicated integrated circuit (unlike the hybrid circuits used in the later Seiko Astron wristwatch). As a result, the BETA 1 prototype set new timekeeping performance records at the International Chronometric Competition held at the Observatory of Neuchâtel in 1967.[13]
Quartz Movement of the Seiko Astron, 1969 (Deutsches Uhrenmuseum, Inv. 2010-006)
The first quartz watch to enter production was the Seiko 35 SQ Astron, which hit the shelves on December 25, 1969. One particularly interesting decision made by Seiko at that time was to not patent the whole movement of the quartz wristwatch, thus allowing other manufacturers to benefit from the Seiko technology. This played a major role in the popularity and quick development of the quartz watch, which in less than a decade was dominant in the watch market, nearly ending an almost 100 years of mechanical wristwatch heritage. The modern quartz movements are produced in very large quantities, and even the cheapest wristwatches typically have quartz movements. Whereas mechanical movements can typically be off by several seconds a day, an inexpensive quartz movement in a child's wristwatch may still be accurate to within half a second per day—ten times better than a mechanical movement.[14]
After a consolidation of the mechanical watch industry in Switzerland during the 1970s, mass production of quartz wristwatches took off under the leadership of the Swatch Group of companies, a Swiss conglomerate with vertical control of the production of Swiss watches and related products. For quartz wristwatches, subsidiaries of Swatch manufactured watch batteries (Renata), oscillators (Oscilloquartz) and integrated circuits (Ebauches Electronic SA). The launch of the new SWATCH brand in 1983, was marked by bold new styling, design and marketing. Today, the Swatch Group is the world's largest watch company.
Seiko's efforts to combine the quartz and mechanical movements bore fruit after 20 years of research, leading to the introduction of the Seiko Spring Drive, first in a limited domestic market production in 1999 and to the world in September 2005. The Spring Drive manages to keep time within quartz standards without the use of a battery, using a traditional mechanical gear train powered by a spring, while at the same time doesn't have the need of a balance wheel either.
Radio time signal watches are a type of electronic quartz watch which synchronizes (time transfer) its time with an external time source such as in atomic clocks, time signals from GPS navigation satellites, the German DCF77 signal in Europe, WWVB in the US, and others. Movements of this type may -among others- synchronize not only the time of day but also the date, the leap-year status of the current year, and the current state of daylight saving time (on or off). However, other than the radio receiver these watches are normal quartz watches in all other aspects.
Electronic watches require electricity as a power source. Some mechanical movements and hybrid electronic-mechanical movements also require electricity. Usually the electricity is provided by a replaceable battery. The first use of electrical power in watches was as a substitute for the mainspring, in order to remove the need for winding. The first electrically powered watch, the Hamilton Electric 500, was released in 1957 by the Hamilton Watch Company of Lancaster, Pennsylvania.
Watch batteries (strictly speaking cells, as a battery is composed of multiple cells) are specially designed for their purpose. They are very small and provide tiny amounts of power continuously for very long periods (several years or more). In most cases, replacing the battery requires a trip to a watch-repair shop or watch dealer; this is especially true for watches that are designed to be water-resistant, as special tools and procedures are required to ensure that the watch remains water-resistant after battery replacement. Silver-oxide and lithium batteries are popular today; mercury batteries, formerly quite common, are no longer used, for environmental reasons. Cheap batteries may be alkaline, of the same size as silver-oxide cells but providing shorter life. Rechargeable batteries are used in some solar powered watches.
Some electronic watches are also powered by the movement of the wearer of the watch. For instance, Seiko's Kinetic powered quartz watches make use of the motion of the wearer's arm turning a rotating weight which causes a tiny generator to supply power to charge a rechargeable battery that runs the watch. The concept is similar to that of self-winding spring movements, except that electrical power is generated instead of mechanical spring tension.
Solar powered watches are powered by light. A photovoltaic cell on the face (dial) of the watch converts light to electricity, which in turn is used to charge a rechargeable battery or capacitor. The movement of the watch draws its power from the rechargeable battery or capacitor. As long as the watch is regularly exposed to fairly strong light (such as sunlight), it never needs battery replacement, and some models need only a few minutes of sunlight to provide weeks of energy (as in the Citizen Eco-Drive). Some of the early solar watches of the 1970s had innovative and unique designs to accommodate the array of solar cells needed to power them (Synchronar, Nepro, Sicura and some models by Cristalonic, Alba, Seiko and Citizen). As the decades progressed and the efficiency of the solar cells increased while the power requirements of the movement and display decreased, solar watches began to be designed to look like other conventional watches.[15]
A rarely used power source is the temperature difference between the wearer's arm and the surrounding environment (as applied in the Citizen Eco-Drive Thermo).
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Display
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Analog
Poljot chronograph
Traditionally, watches have displayed the time in analog form, with a numbered dial upon which are mounted at least a rotating hour hand and a longer, rotating minute hand. Many watches also incorporate a third hand that shows the current second of the current minute. Watches powered by quartz usually have a second hand that snaps every second to the next marker. Watches powered by a mechanical movement appears to have a gliding second hand, although it is actually not gliding; the hand merely moves in smaller steps, typically 1/5 of a second, corresponding to the beat (half period) of the balance wheel. In some escapements (for example the duplex escapement), the hand advances every two beats (full period) of the balance wheel, typically 1/2 second in those watches, or even every four beats (two periods, 1 second), in the double duplex escapement. A truly gliding second hand is achieved with the tri-synchro regulator of Spring Drive watches. All of the hands are normally mechanical, physically rotating on the dial, although a few watches have been produced with "hands" that are simulated by a liquid-crystal display.
Analog display of the time is nearly universal in watches sold as jewelry or collectibles, and in these watches, the range of different styles of hands, numbers, and other aspects of the analog dial is very broad. In watches sold for timekeeping, analog display remains very popular, as many people find it easier to read than digital display; but in timekeeping watches the emphasis is on clarity and accurate reading of the time under all conditions (clearly marked digits, easily visible hands, large watch faces, etc.). They are specifically designed for the left wrist with the stem (the knob used for changing the time) on the right side of the watch; this makes it easy to change the time without removing the watch from the wrist. This is the case if one is right-handed and the watch is worn on the left wrist (as is traditionally done). If one is left-handed and wears the watch on the right wrist, one has to remove the watch from the wrist to reset the time or to wind the watch.
Analog watches as well as clocks are often marketed showing a display time of approximately 10:09 or 10:10. This creates a visually pleasing smile-like face on upper half of the watch, in addition to enclosing the manufacturer's name. Digital displays often show a time of 12:08, where the increases in the numbers from left to right culminating in the fully lit numerical display of the 8 also gives a positive feeling.[16][17]
Analog watch displays can be used to indicate cardinal direction due to the relation between the position of the hour hand and the position of the Sun in the sky. By rotating the watch so that the hour hand points toward the Sun, the point halfway between the hour hand and 12 o'clock will indicate south when observing from a position in the Northern hemisphere. In the Southern hemisphere, the point halfway between the hour hand pointed at the sun and 12 o'clock on the dial indicates North.
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Digital
Cortébert digital mechanical pocket watch. 1890s
Cortébert digital mechanical wristwatch. 1920s
A silver Pulsar LED watch from 1976.
A digital display simply shows the time as a number, e.g., 12:08 instead of a short hand pointing towards the number 12 and a long hand 8/60 of the way round the dial. The digits are usually shown as a seven-segment display.
The first digital mechanical pocket watches appeared in late 19th century. In the 1920s the first digital mechanical wristwatches appeared.
The first digital electronic watch, a Pulsar LED prototype in 1970, was developed jointly by Hamilton Watch Company and Electro-Data. John Bergey, the head of Hamilton's Pulsar division, said that he was inspired to make a digital timepiece by the then-futuristic digital clock that Hamilton themselves made for the 1968 science fiction film 2001: A Space Odyssey. On April 4, 1972, the Pulsar was finally ready, made in 18-carat gold and sold for $2,100. It had a red light-emitting diode (LED) display.
Digital LED watches were very expensive and out of reach to the common consumer until 1975, when Texas Instruments started to mass produce LED watches inside a plastic case. These watches, which first retailed for only $20,[18] reduced to $10 in 1976, saw Pulsar lose $6 million and the Pulsar brand sold to Seiko.[19]
An early LED watch that was rather problematic was The Black Watch made and sold by British company Sinclair Research in 1975. This was only sold for a few years, as production problems and returned (faulty) product forced the company to cease production.
A digital watch displaying the time, seconds, and date
Most watches with LED displays required that the user press a button to see the time displayed for a few seconds, because LEDs used so much power that they could not be kept operating continuously. Usually the LED display color would be red. Watches with LED displays were popular for a few years, but soon the LED displays were superseded by liquid crystal displays (LCDs), which used less battery power and were much more convenient in use, with the display always visible and no need to push a button before seeing the time. Only in darkness you had to press a button to lit the display with a tiny light bulb, later illuminating LEDs. The first LCD watch with a six-digit LCD was the 1973 Seiko 06LC, although various forms of early LCD watches with a four-digit display were marketed as early as 1972 including the 1972 Gruen Teletime LCD Watch, and the Cox Electronic Systems Quarza.[20] In Switzerland, Ebauches Electronic SA presented a prototype eight-digit LCD wristwatch showing time and date at the MUBA Fair, Basle, in March 1973, using a Twisted Nematic LCD manufactured by Brown, Boveri & Cie, Switzerland, which became the supplier of LCDs to Casio for the CASIOTRON watch in 1974.[21]
From the 1980s onward, digital watch technology vastly improved. In 1982 Seiko produced a watch with a small television screen built in[22], and Casio produced a digital watch with a thermometer as well as another that could translate 1,500 Japanese words into English. In 1985, Casio produced the CFX-400 scientific calculator watch. In 1987 Casio produced a watch that could dial your telephone number and Citizen revealed one that would react to your voice. In 1995 Timex released a watch which allowed the wearer to download and store data from a computer to their wrist. Some watches, such as the Timex Datalink USB, feature dot matrix displays. Since their apex during the late 1980s to mid 1990s high technology fad, digital watches have mostly become simpler, less expensive time pieces with little variety between models.
Despite these many advances, almost all watches with digital displays are used as timekeeping watches. Expensive watches for collectors rarely have digital displays since there is little demand for them. Less craftsmanship is required to make a digital watch face and most collectors find that analog dials (especially with complications) vary in quality more than digital dials due to the details and finishing of the parts that make up the dial (thus making the differences between a cheap and expensive watch more evident).
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Functions
The Rolex Submariner, an officially certified chronometer
All watches provide the time of day, giving at least the hour and minute, and usually the second. Most also provide the current date, and often the day of the week as well. However, many watches also provide a great deal of information beyond the basics of time and date. Some watches include alarms. Other elaborate and more expensive watches, both pocket and wrist models, also incorporate striking mechanisms or repeater functions, so that the wearer could learn the time by the sound emanating from the watch. This announcement or striking feature is an essential characteristic of true clocks and distinguishes such watches from ordinary timepieces. This feature is available on most digital watches.
A complicated watch has one or more functions beyond the basic function of displaying the time and the date; such a functionality is called a complication. Two popular complications are the chronograph complication, which is the ability of the watch movement to function as a stopwatch, and the moonphase complication, which is a display of the lunar phase. Other more expensive complications include Tourbillon, Perpetual calendar, Minute repeater, and Equation of time. A truly complicated watch has many of these complications at once (see Calibre 89 from Patek Philippe for instance). Some watches can both indicate the direction of Mecca[23] and have alarms that can be set for all daily prayer requirements[24] . Among watch enthusiasts, complicated watches are especially collectible. Some watches include a second 12-hour display for UTC (as Pontos Grand Guichet GMT).
The similar-sounding terms chronograph and chronometer are often confused, although they mean altogether different things. A chronograph has a stopwatch complication, as explained above, while a chronometer watch has a high quality mechanical or a thermo-compensated movement that has been tested and certified to operate within a certain standard of accuracy by the COSC (Contrôle Officiel Suisse des Chronomètres). The concepts are different but not mutually exclusive; so a watch can be a chronograph, a chronometer, both, or neither.
Timex Datalink USB Dress edition from 2003 with a dot matrix display; the Invasion video game is on the screen
Many computerized wristwatches have been developed, but none have had long-term sales success, because they have awkward user interfaces due to the tiny screens and buttons, and a short battery life. As miniaturized electronics became cheaper, watches have been developed containing calculators, tonometers, barometers, altimeters, a compass using both hands to show the N/S direction, video games, digital cameras, keydrives, GPS receivers and cellular phones. In the early 1980s Seiko marketed a watch with a television in it. Such watches have also had the reputation as unsightly and thus mainly geek toys. Several companies have however attempted to develop a computer contained in a wristwatch (see also wearable computer).
Braille watches have analog displays with raised bumps around the face to allow blind users to tell the time. Their digital equivalents use synthesised speech to speak the time on command.
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Uses
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Fashion
A sapphire cabochon on the crown of a men's dress watch
Wristwatches are often appreciated as jewelry or as collectible works of art rather than just as timepieces. This has created several different markets for wristwatches, ranging from very inexpensive but accurate watches (intended for no other purpose than telling the correct time) to extremely expensive watches that serve mainly as personal adornment (featuring jewel bearings to hold gemstones) or as examples of high achievement in miniaturization and precision mechanical engineering.
Traditionally, men's dress watches appropriate for informal (business), semi-formal, and formal attire are gold, thin, simple, and plain, but increasingly rugged, complicated, or sports watches are considered acceptable for such attire. Some dress watches have a cabochon on the crown and many women's dress watches have faceted gemstones on the face, bezel, or bracelet. Some are made entirely of facetted sapphire (corundum)[25].
Many fashion and department stores offer a variety of less-expensive, trendy, "costume" watches (usually for women), many of which are similar in quality to basic quartz timepieces but which feature bolder designs. In the 1980s, the Swiss Swatch company hired graphic designers to redesign a new annual collection of non-repairable watches.
Most companies that produce watches specialize in one or some of these markets. Companies such as Patek Philippe, Blancpain and Jaeger-LeCoultre specialize in simple and complicated mechanical dress watches; companies such as Omega SA, Ball Watch Company, TAG Heuer, Sinn, Breitling, Panerai and Rolex specialize in rugged, reliable mechanical watches for sport and aviation use. Companies such as Casio, Timex, and Seiko specialize in watches as affordable timepieces or multifunctional computers.
Trade in counterfeit watches, which mimic expensive brand-name watches, constitutes an estimated US$1 billion market per year.[26]
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Space
The Omega Speedmaster, selected by U.S. space agencies
Zero gravity environment and other extreme conditions encountered by astronauts in space requires the use of specially tested watches. On April 12, 1961, Yuri Gagarin wore a Shturmanskie (a transliteration of Штурманские which actually means "navigator's") wristwatch during his historic first flight into space. The Shturmanskie was manufactured at the First Moscow Factory. Since 1964, the watches of the First Moscow Factory have been marked by the trademark "ПОЛЕТ", transliterated as "POLJOT", which means "flight" in Russian and is a tribute to the many space trips its watches have accomplished. In the late 1970s, Poljot launched a new chrono movement, the 3133. With a 23 jewel movement and manual winding (43 hours), it was a modified Russian version of the Swiss Valjoux 7734 of the early 1970s. Poljot 3133 were taken into space by astronauts from Russia, France, Germany and Ukraine. On the arm of Valeriy Polyakov, a Poljot 3133 chronograph movement-based watch set a space record for the longest space flight in history.[27]
Astronaut Nancy J. Currie wears the Timex Ironman Triathlon Datalink model 78401 during STS 88.
Through the 1960s, a large range of watches were tested for durability and precision under extreme temperature changes and vibrations. The Omega Speedmaster Professional was selected by NASA, the U.S. space agency. Heuer became the first Swiss watch in space thanks to a Heuer Stopwatch, worn by John Glenn in 1962 when he piloted the Friendship 7 on the first manned U.S. orbital mission. The Breitling Navitimer Cosmonaute was designed with a 24-hour analog dial to avoid confusion between AM and PM, which are meaningless in space. It was first worn in space by U.S. astronaut Scott Carpenter on May 24, 1962 in the Aurora 7 mercury capsule.[28] Since 1994 Fortis is the exclusive supplier for manned space missions authorized by the Russian Federal Space Agency. China National Space Administration (CNSA) astronauts wear the Fiyta[29] spacewatches. At BaselWorld, 2008, Seiko announced the creation of the first watch ever designed specifically for a space walk, Spring Drive Spacewalk. Timex Datalink is flight certified by NASA for space missions and is one of the watches qualified by NASA for space travel. Both the Casio G-Shock DW-5600C and 5600E are Flight-Qualified for NASA space travel.[30][31][32][33] The various Datalink models were used both by cosmonauts and astronauts.
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Scuba diving
Seiko 7002-7020 Diver's 200 m on a 4-ring NATO style strap
Watches may be crafted to become water resistant. These watches are sometimes called diving watches when they are suitable for scuba diving or saturation diving. The International Organization for Standardization issued a standard for water resistant watches which also prohibits the term "waterproof" to be used with watches, which many countries have adopted.
Water resistance is achieved by the gaskets which forms a watertight seal, used in conjunction with a sealant applied on the case to help keep water out. The material of the case must also be tested in order to pass as water resistant.[34]
None of the tests defined by ISO 2281 for the Water Resistant mark are suitable to qualify a watch for scuba diving. Such watches are designed for everyday life and must be water resistant during exercises such as swimming. They can be worn in different temperature and pressure conditions but are under no circumstances designed for scuba diving.
The standards for diving watches are regulated by the ISO 6425 international standard. The watches are tested in static or still water under 125% of the rated (water)pressure, thus a watch with a 200 metre rating will be water resistant if it is stationary and under 250 metres of static water. The testing of the water resistance is fundamentally different from non-dive watches, because every watch has to be fully tested. Besides water resistance standards to a minimum of 100 metre depth rating ISO 6425 also provides eight minimum requirements for mechanical diver's watches for scuba diving (quartz and digital watches have slightly differing readability requirements). For diver's watches for mixed-gas saturation diving two additional requirements have to be met.
Watches are classified by their degree of water resistance, which roughly translates to the following (1 metre = 3.281 feet):[35]
Main Article ISO 6425
Water resistance rating Suitability Remarks
Water Resistant or 30 m Suitable for everyday use. Splash/rain resistant. NOT suitable for swimming, snorkelling, water related work and fishing. NOT suitable for diving.
Water Resistant 50 m Suitable for swimming, white water rafting, non-snorkeling water related work, and fishing. NOT suitable for diving.
Water Resistant 100 m Suitable for recreational surfing, swimming, snorkeling, sailing and water sports. not suitable for diving. This is the standard for children's digital watches.
Water Resistant 200 m Suitable for professional marine activity and serious surface water sports. suitable for diving.
Diver's 100 m Minimum ISO standard for scuba diving at depths not requiring helium gas. Diver's 100 m and 150 m watches are generally old(er) watches.
Diver's 200 m or 300 m Suitable for scuba diving at depths not requiring helium gas. Typical ratings for contemporary diver's watches.
Diver's 300+ m helium safe Suitable for saturation diving (helium enriched environment). Watches designed for helium mixed-gas diving will have additional markings to point this out.
Some watches use bar instead of meters, which may then be multiplied by 10, and then subtracted by 10. This is because 1 bar is equal to one atmosphere or 10 metres of water (therefore 1 bar at the surface and one more each 10 metres). to be approximately equal to the rating based on metres. Therefore, a 5 bar watch is equivalent to a 40 metre watch. Some watches are rated in atmospheres (atm), which are roughly equivalent to bar.
Before wristwatches became popular in the 1920s, most watches were pocket watches, which often had covers and were carried in a pocket and attached to a watch chain or watch fob.[3] In the early 1900s, the wristwatch, originally called a Wristlet, was reserved for women and considered more of a passing fad than a serious timepiece. Real gentlemen, who carried pocket watches, were actually quoted as saying they would "sooner wear a skirt as wear a wristwatch"[4]. This all changed in World War I when soldiers on the battlefield found using a pocket watch to be impractical, so they attached the pocket watch to their wrist by a cupped leather strap. It is also believed that Girard-Perregaux equipped the German Imperial Navy in a similar fashion as early as the 1880s, which were used while synchronizing naval attacks and firing artillery.[4]
Most inexpensive and medium-priced watches used mainly for timekeeping are electronic watches with quartz movements.[1] Expensive, collectible watches valued more for their workmanship and aesthetic appeal than for simple timekeeping, often have purely mechanical movements and are powered by springs, even though mechanical movements are less accurate than more affordable quartz movements. In addition to the time, modern watches often display the day, date, month and year, and electronic watches may have many other functions. Watches that provide additional time-related features such as timers, chronographs and alarm functions are not uncommon. Some modern designs even go as far as using GPS[5] technology or heart-rate monitoring[6] capabilities.
History
The earliest dated watch known, from 1530
Main article: History of watches
See also: History of timekeeping devices This section requires expansion.
Watches evolved from portable spring driven clocks, which first appeared in 15th century Europe. Watches weren't widely worn in pockets until the 17th century.
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Movement
Different kinds of movements move the hands differently as shown in this 2 second exposure. The left watch has a mechanical 1/6 s movement, the right one has a "1 s" quartz movement
A Russian mechanical watch movement
A movement in watchmaking is the mechanism that measures the passage of time and displays the current time (and possibly other information including date, month and day). Movements may be entirely mechanical, entirely electronic (potentially with no moving parts), or a blend of the two. Most watches intended mainly for timekeeping today have electronic movements, with mechanical hands on the watch face indicating the time.
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Mechanical movements
Main article: Mechanical watch
Compared to electronic movements, mechanical watches are less accurate, often with errors of seconds per day, and they are sensitive to position, temperature[7] and magnetism.[8] They are also costly to produce, require regular maintenance and adjustment, and are more prone to failure. Nevertheless, the craftsmanship of mechanical watches still attracts interest from part of the watch-buying public. Skeleton watches are designed to leave the mechanism visible for aesthetic purposes.
Mechanical movements use an escapement mechanism to control and limit the unwinding and winding parts of a spring, converting what would otherwise be a simple unwinding into a controlled and periodic energy release. Mechanical movements also use a balance wheel together with the balance spring (also known as a hairspring) to control motion of the gear system of the watch in a manner analogous to the pendulum of a pendulum clock. The tourbillon, an optional part for mechanical movements, is a rotating frame for the escapement, which is used to cancel out or reduce the effects of gravitational bias to the timekeeping. Due to the complexity of designing a tourbillon, they are very expensive, and only found in "prestige" watches.[1]
The pin-lever escapement (called the Roskopf movement after its inventor, Georges Frederic Roskopf), which is a cheaper version of the fully levered movement, was manufactured in huge quantities by many Swiss manufacturers as well as Timex, until it was replaced by quartz movements.[9][10][11]
Tuning-fork watches use a type of electromechanical movement. Introduced by Bulova in 1960, they use a tuning fork with a precise frequency (most often 360 hertz) to drive a mechanical watch. The task of converting electronically pulsed fork vibration into rotary movement is done via two tiny jeweled fingers, called pawls. Tuning-fork watches were rendered obsolete when electronic quartz watches were developed. Quartz watches were cheaper to produce and even more accurate.
Main article: Mainspring
Traditional mechanical watch movements use a spiral spring called a mainspring as a power source. In manual watches the spring must be rewound periodically by the user by turning the watch crown. Antique pocketwatches were wound by inserting a separate key into a hole in the back of the watch and turning it. Most modern watches are designed to run 40 hours on a winding and thus must be wound daily, but some run for several days and a few have 192-hour mainsprings and are wound weekly.
Main article: Automatic watch
Automatic watch: An eccentric weight, called a rotor, swings with the movement of the wearer's body and winds the spring
A self-winding or automatic watches is one that rewinds the mainspring of a mechanical movement by the natural motions of the wearer's body. The first self-winding mechanism was invented for pocketwatches in 1770 by Abraham-Louis Perrelet,[12] but the first "self-winding", or "automatic", wristwatch was the invention of a British watch repairer named John Harwood in 1923. This type of watch allows for constant winding without special action from the wearer; it works by an eccentric weight, called a winding rotor, which rotates with the movement of the wearer's wrist. The back-and-forth motion of the winding rotor couples to a ratchet to automatically wind the mainspring. Self-winding watches usually can also be wound manually so they can be kept running when not worn or if the wearer's wrist motions are inadequate to keep the watch wound.
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Electronic movements
See also: Electric watch
Electronic movements have few or no moving parts, as they use the piezoelectric effect in a tiny quartz crystal to provide a stable time base for a mostly electronic movement. The crystal forms a quartz oscillator which resonates at a specific and highly stable frequency, and which can be used to accurately pace a timekeeping mechanism. For this reason, electronic watches are often called quartz watches. Most quartz movements are primarily electronic but are geared to drive mechanical hands on the face of the watch in order to provide a traditional analog display of the time, which is still preferred by some consumers.
Prototype of a Quartz Wristwatch, CEH Switzerland, 1967
In 1959 Seiko gave an order to Epson (a daughter company of Seiko and the actual brain behind the quartz revolution) to start developing a quartz wristwatch. The project was codenamed 59A and by the 1964 Tokyo Summer Olympics, Seiko had a working prototype of a portable quartz watch which took part in time measurements throughout the event.
The first prototypes of an electronic quartz wristwatch (not just portable quartz watches as the Seiko timekeeping devices at the Tokyo Olympics in 1964) were made by the CEH research laboratory in Neuchâtel, Switzerland. From 1965 through 1967 pioneering development work was done on a miniaturized 8192 Hz quartz oscillator, a thermo-compensation module and an inhouse-made, dedicated integrated circuit (unlike the hybrid circuits used in the later Seiko Astron wristwatch). As a result, the BETA 1 prototype set new timekeeping performance records at the International Chronometric Competition held at the Observatory of Neuchâtel in 1967.[13]
Quartz Movement of the Seiko Astron, 1969 (Deutsches Uhrenmuseum, Inv. 2010-006)
The first quartz watch to enter production was the Seiko 35 SQ Astron, which hit the shelves on December 25, 1969. One particularly interesting decision made by Seiko at that time was to not patent the whole movement of the quartz wristwatch, thus allowing other manufacturers to benefit from the Seiko technology. This played a major role in the popularity and quick development of the quartz watch, which in less than a decade was dominant in the watch market, nearly ending an almost 100 years of mechanical wristwatch heritage. The modern quartz movements are produced in very large quantities, and even the cheapest wristwatches typically have quartz movements. Whereas mechanical movements can typically be off by several seconds a day, an inexpensive quartz movement in a child's wristwatch may still be accurate to within half a second per day—ten times better than a mechanical movement.[14]
After a consolidation of the mechanical watch industry in Switzerland during the 1970s, mass production of quartz wristwatches took off under the leadership of the Swatch Group of companies, a Swiss conglomerate with vertical control of the production of Swiss watches and related products. For quartz wristwatches, subsidiaries of Swatch manufactured watch batteries (Renata), oscillators (Oscilloquartz) and integrated circuits (Ebauches Electronic SA). The launch of the new SWATCH brand in 1983, was marked by bold new styling, design and marketing. Today, the Swatch Group is the world's largest watch company.
Seiko's efforts to combine the quartz and mechanical movements bore fruit after 20 years of research, leading to the introduction of the Seiko Spring Drive, first in a limited domestic market production in 1999 and to the world in September 2005. The Spring Drive manages to keep time within quartz standards without the use of a battery, using a traditional mechanical gear train powered by a spring, while at the same time doesn't have the need of a balance wheel either.
Radio time signal watches are a type of electronic quartz watch which synchronizes (time transfer) its time with an external time source such as in atomic clocks, time signals from GPS navigation satellites, the German DCF77 signal in Europe, WWVB in the US, and others. Movements of this type may -among others- synchronize not only the time of day but also the date, the leap-year status of the current year, and the current state of daylight saving time (on or off). However, other than the radio receiver these watches are normal quartz watches in all other aspects.
Electronic watches require electricity as a power source. Some mechanical movements and hybrid electronic-mechanical movements also require electricity. Usually the electricity is provided by a replaceable battery. The first use of electrical power in watches was as a substitute for the mainspring, in order to remove the need for winding. The first electrically powered watch, the Hamilton Electric 500, was released in 1957 by the Hamilton Watch Company of Lancaster, Pennsylvania.
Watch batteries (strictly speaking cells, as a battery is composed of multiple cells) are specially designed for their purpose. They are very small and provide tiny amounts of power continuously for very long periods (several years or more). In most cases, replacing the battery requires a trip to a watch-repair shop or watch dealer; this is especially true for watches that are designed to be water-resistant, as special tools and procedures are required to ensure that the watch remains water-resistant after battery replacement. Silver-oxide and lithium batteries are popular today; mercury batteries, formerly quite common, are no longer used, for environmental reasons. Cheap batteries may be alkaline, of the same size as silver-oxide cells but providing shorter life. Rechargeable batteries are used in some solar powered watches.
Some electronic watches are also powered by the movement of the wearer of the watch. For instance, Seiko's Kinetic powered quartz watches make use of the motion of the wearer's arm turning a rotating weight which causes a tiny generator to supply power to charge a rechargeable battery that runs the watch. The concept is similar to that of self-winding spring movements, except that electrical power is generated instead of mechanical spring tension.
Solar powered watches are powered by light. A photovoltaic cell on the face (dial) of the watch converts light to electricity, which in turn is used to charge a rechargeable battery or capacitor. The movement of the watch draws its power from the rechargeable battery or capacitor. As long as the watch is regularly exposed to fairly strong light (such as sunlight), it never needs battery replacement, and some models need only a few minutes of sunlight to provide weeks of energy (as in the Citizen Eco-Drive). Some of the early solar watches of the 1970s had innovative and unique designs to accommodate the array of solar cells needed to power them (Synchronar, Nepro, Sicura and some models by Cristalonic, Alba, Seiko and Citizen). As the decades progressed and the efficiency of the solar cells increased while the power requirements of the movement and display decreased, solar watches began to be designed to look like other conventional watches.[15]
A rarely used power source is the temperature difference between the wearer's arm and the surrounding environment (as applied in the Citizen Eco-Drive Thermo).
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Display
[edit]
Analog
Poljot chronograph
Traditionally, watches have displayed the time in analog form, with a numbered dial upon which are mounted at least a rotating hour hand and a longer, rotating minute hand. Many watches also incorporate a third hand that shows the current second of the current minute. Watches powered by quartz usually have a second hand that snaps every second to the next marker. Watches powered by a mechanical movement appears to have a gliding second hand, although it is actually not gliding; the hand merely moves in smaller steps, typically 1/5 of a second, corresponding to the beat (half period) of the balance wheel. In some escapements (for example the duplex escapement), the hand advances every two beats (full period) of the balance wheel, typically 1/2 second in those watches, or even every four beats (two periods, 1 second), in the double duplex escapement. A truly gliding second hand is achieved with the tri-synchro regulator of Spring Drive watches. All of the hands are normally mechanical, physically rotating on the dial, although a few watches have been produced with "hands" that are simulated by a liquid-crystal display.
Analog display of the time is nearly universal in watches sold as jewelry or collectibles, and in these watches, the range of different styles of hands, numbers, and other aspects of the analog dial is very broad. In watches sold for timekeeping, analog display remains very popular, as many people find it easier to read than digital display; but in timekeeping watches the emphasis is on clarity and accurate reading of the time under all conditions (clearly marked digits, easily visible hands, large watch faces, etc.). They are specifically designed for the left wrist with the stem (the knob used for changing the time) on the right side of the watch; this makes it easy to change the time without removing the watch from the wrist. This is the case if one is right-handed and the watch is worn on the left wrist (as is traditionally done). If one is left-handed and wears the watch on the right wrist, one has to remove the watch from the wrist to reset the time or to wind the watch.
Analog watches as well as clocks are often marketed showing a display time of approximately 10:09 or 10:10. This creates a visually pleasing smile-like face on upper half of the watch, in addition to enclosing the manufacturer's name. Digital displays often show a time of 12:08, where the increases in the numbers from left to right culminating in the fully lit numerical display of the 8 also gives a positive feeling.[16][17]
Analog watch displays can be used to indicate cardinal direction due to the relation between the position of the hour hand and the position of the Sun in the sky. By rotating the watch so that the hour hand points toward the Sun, the point halfway between the hour hand and 12 o'clock will indicate south when observing from a position in the Northern hemisphere. In the Southern hemisphere, the point halfway between the hour hand pointed at the sun and 12 o'clock on the dial indicates North.
[edit]
Digital
Cortébert digital mechanical pocket watch. 1890s
Cortébert digital mechanical wristwatch. 1920s
A silver Pulsar LED watch from 1976.
A digital display simply shows the time as a number, e.g., 12:08 instead of a short hand pointing towards the number 12 and a long hand 8/60 of the way round the dial. The digits are usually shown as a seven-segment display.
The first digital mechanical pocket watches appeared in late 19th century. In the 1920s the first digital mechanical wristwatches appeared.
The first digital electronic watch, a Pulsar LED prototype in 1970, was developed jointly by Hamilton Watch Company and Electro-Data. John Bergey, the head of Hamilton's Pulsar division, said that he was inspired to make a digital timepiece by the then-futuristic digital clock that Hamilton themselves made for the 1968 science fiction film 2001: A Space Odyssey. On April 4, 1972, the Pulsar was finally ready, made in 18-carat gold and sold for $2,100. It had a red light-emitting diode (LED) display.
Digital LED watches were very expensive and out of reach to the common consumer until 1975, when Texas Instruments started to mass produce LED watches inside a plastic case. These watches, which first retailed for only $20,[18] reduced to $10 in 1976, saw Pulsar lose $6 million and the Pulsar brand sold to Seiko.[19]
An early LED watch that was rather problematic was The Black Watch made and sold by British company Sinclair Research in 1975. This was only sold for a few years, as production problems and returned (faulty) product forced the company to cease production.
A digital watch displaying the time, seconds, and date
Most watches with LED displays required that the user press a button to see the time displayed for a few seconds, because LEDs used so much power that they could not be kept operating continuously. Usually the LED display color would be red. Watches with LED displays were popular for a few years, but soon the LED displays were superseded by liquid crystal displays (LCDs), which used less battery power and were much more convenient in use, with the display always visible and no need to push a button before seeing the time. Only in darkness you had to press a button to lit the display with a tiny light bulb, later illuminating LEDs. The first LCD watch with a six-digit LCD was the 1973 Seiko 06LC, although various forms of early LCD watches with a four-digit display were marketed as early as 1972 including the 1972 Gruen Teletime LCD Watch, and the Cox Electronic Systems Quarza.[20] In Switzerland, Ebauches Electronic SA presented a prototype eight-digit LCD wristwatch showing time and date at the MUBA Fair, Basle, in March 1973, using a Twisted Nematic LCD manufactured by Brown, Boveri & Cie, Switzerland, which became the supplier of LCDs to Casio for the CASIOTRON watch in 1974.[21]
From the 1980s onward, digital watch technology vastly improved. In 1982 Seiko produced a watch with a small television screen built in[22], and Casio produced a digital watch with a thermometer as well as another that could translate 1,500 Japanese words into English. In 1985, Casio produced the CFX-400 scientific calculator watch. In 1987 Casio produced a watch that could dial your telephone number and Citizen revealed one that would react to your voice. In 1995 Timex released a watch which allowed the wearer to download and store data from a computer to their wrist. Some watches, such as the Timex Datalink USB, feature dot matrix displays. Since their apex during the late 1980s to mid 1990s high technology fad, digital watches have mostly become simpler, less expensive time pieces with little variety between models.
Despite these many advances, almost all watches with digital displays are used as timekeeping watches. Expensive watches for collectors rarely have digital displays since there is little demand for them. Less craftsmanship is required to make a digital watch face and most collectors find that analog dials (especially with complications) vary in quality more than digital dials due to the details and finishing of the parts that make up the dial (thus making the differences between a cheap and expensive watch more evident).
[edit]
Functions
The Rolex Submariner, an officially certified chronometer
All watches provide the time of day, giving at least the hour and minute, and usually the second. Most also provide the current date, and often the day of the week as well. However, many watches also provide a great deal of information beyond the basics of time and date. Some watches include alarms. Other elaborate and more expensive watches, both pocket and wrist models, also incorporate striking mechanisms or repeater functions, so that the wearer could learn the time by the sound emanating from the watch. This announcement or striking feature is an essential characteristic of true clocks and distinguishes such watches from ordinary timepieces. This feature is available on most digital watches.
A complicated watch has one or more functions beyond the basic function of displaying the time and the date; such a functionality is called a complication. Two popular complications are the chronograph complication, which is the ability of the watch movement to function as a stopwatch, and the moonphase complication, which is a display of the lunar phase. Other more expensive complications include Tourbillon, Perpetual calendar, Minute repeater, and Equation of time. A truly complicated watch has many of these complications at once (see Calibre 89 from Patek Philippe for instance). Some watches can both indicate the direction of Mecca[23] and have alarms that can be set for all daily prayer requirements[24] . Among watch enthusiasts, complicated watches are especially collectible. Some watches include a second 12-hour display for UTC (as Pontos Grand Guichet GMT).
The similar-sounding terms chronograph and chronometer are often confused, although they mean altogether different things. A chronograph has a stopwatch complication, as explained above, while a chronometer watch has a high quality mechanical or a thermo-compensated movement that has been tested and certified to operate within a certain standard of accuracy by the COSC (Contrôle Officiel Suisse des Chronomètres). The concepts are different but not mutually exclusive; so a watch can be a chronograph, a chronometer, both, or neither.
Timex Datalink USB Dress edition from 2003 with a dot matrix display; the Invasion video game is on the screen
Many computerized wristwatches have been developed, but none have had long-term sales success, because they have awkward user interfaces due to the tiny screens and buttons, and a short battery life. As miniaturized electronics became cheaper, watches have been developed containing calculators, tonometers, barometers, altimeters, a compass using both hands to show the N/S direction, video games, digital cameras, keydrives, GPS receivers and cellular phones. In the early 1980s Seiko marketed a watch with a television in it. Such watches have also had the reputation as unsightly and thus mainly geek toys. Several companies have however attempted to develop a computer contained in a wristwatch (see also wearable computer).
Braille watches have analog displays with raised bumps around the face to allow blind users to tell the time. Their digital equivalents use synthesised speech to speak the time on command.
[edit]
Uses
[edit]
Fashion
A sapphire cabochon on the crown of a men's dress watch
Wristwatches are often appreciated as jewelry or as collectible works of art rather than just as timepieces. This has created several different markets for wristwatches, ranging from very inexpensive but accurate watches (intended for no other purpose than telling the correct time) to extremely expensive watches that serve mainly as personal adornment (featuring jewel bearings to hold gemstones) or as examples of high achievement in miniaturization and precision mechanical engineering.
Traditionally, men's dress watches appropriate for informal (business), semi-formal, and formal attire are gold, thin, simple, and plain, but increasingly rugged, complicated, or sports watches are considered acceptable for such attire. Some dress watches have a cabochon on the crown and many women's dress watches have faceted gemstones on the face, bezel, or bracelet. Some are made entirely of facetted sapphire (corundum)[25].
Many fashion and department stores offer a variety of less-expensive, trendy, "costume" watches (usually for women), many of which are similar in quality to basic quartz timepieces but which feature bolder designs. In the 1980s, the Swiss Swatch company hired graphic designers to redesign a new annual collection of non-repairable watches.
Most companies that produce watches specialize in one or some of these markets. Companies such as Patek Philippe, Blancpain and Jaeger-LeCoultre specialize in simple and complicated mechanical dress watches; companies such as Omega SA, Ball Watch Company, TAG Heuer, Sinn, Breitling, Panerai and Rolex specialize in rugged, reliable mechanical watches for sport and aviation use. Companies such as Casio, Timex, and Seiko specialize in watches as affordable timepieces or multifunctional computers.
Trade in counterfeit watches, which mimic expensive brand-name watches, constitutes an estimated US$1 billion market per year.[26]
[edit]
Space
The Omega Speedmaster, selected by U.S. space agencies
Zero gravity environment and other extreme conditions encountered by astronauts in space requires the use of specially tested watches. On April 12, 1961, Yuri Gagarin wore a Shturmanskie (a transliteration of Штурманские which actually means "navigator's") wristwatch during his historic first flight into space. The Shturmanskie was manufactured at the First Moscow Factory. Since 1964, the watches of the First Moscow Factory have been marked by the trademark "ПОЛЕТ", transliterated as "POLJOT", which means "flight" in Russian and is a tribute to the many space trips its watches have accomplished. In the late 1970s, Poljot launched a new chrono movement, the 3133. With a 23 jewel movement and manual winding (43 hours), it was a modified Russian version of the Swiss Valjoux 7734 of the early 1970s. Poljot 3133 were taken into space by astronauts from Russia, France, Germany and Ukraine. On the arm of Valeriy Polyakov, a Poljot 3133 chronograph movement-based watch set a space record for the longest space flight in history.[27]
Astronaut Nancy J. Currie wears the Timex Ironman Triathlon Datalink model 78401 during STS 88.
Through the 1960s, a large range of watches were tested for durability and precision under extreme temperature changes and vibrations. The Omega Speedmaster Professional was selected by NASA, the U.S. space agency. Heuer became the first Swiss watch in space thanks to a Heuer Stopwatch, worn by John Glenn in 1962 when he piloted the Friendship 7 on the first manned U.S. orbital mission. The Breitling Navitimer Cosmonaute was designed with a 24-hour analog dial to avoid confusion between AM and PM, which are meaningless in space. It was first worn in space by U.S. astronaut Scott Carpenter on May 24, 1962 in the Aurora 7 mercury capsule.[28] Since 1994 Fortis is the exclusive supplier for manned space missions authorized by the Russian Federal Space Agency. China National Space Administration (CNSA) astronauts wear the Fiyta[29] spacewatches. At BaselWorld, 2008, Seiko announced the creation of the first watch ever designed specifically for a space walk, Spring Drive Spacewalk. Timex Datalink is flight certified by NASA for space missions and is one of the watches qualified by NASA for space travel. Both the Casio G-Shock DW-5600C and 5600E are Flight-Qualified for NASA space travel.[30][31][32][33] The various Datalink models were used both by cosmonauts and astronauts.
[edit]
Scuba diving
Seiko 7002-7020 Diver's 200 m on a 4-ring NATO style strap
Watches may be crafted to become water resistant. These watches are sometimes called diving watches when they are suitable for scuba diving or saturation diving. The International Organization for Standardization issued a standard for water resistant watches which also prohibits the term "waterproof" to be used with watches, which many countries have adopted.
Water resistance is achieved by the gaskets which forms a watertight seal, used in conjunction with a sealant applied on the case to help keep water out. The material of the case must also be tested in order to pass as water resistant.[34]
None of the tests defined by ISO 2281 for the Water Resistant mark are suitable to qualify a watch for scuba diving. Such watches are designed for everyday life and must be water resistant during exercises such as swimming. They can be worn in different temperature and pressure conditions but are under no circumstances designed for scuba diving.
The standards for diving watches are regulated by the ISO 6425 international standard. The watches are tested in static or still water under 125% of the rated (water)pressure, thus a watch with a 200 metre rating will be water resistant if it is stationary and under 250 metres of static water. The testing of the water resistance is fundamentally different from non-dive watches, because every watch has to be fully tested. Besides water resistance standards to a minimum of 100 metre depth rating ISO 6425 also provides eight minimum requirements for mechanical diver's watches for scuba diving (quartz and digital watches have slightly differing readability requirements). For diver's watches for mixed-gas saturation diving two additional requirements have to be met.
Watches are classified by their degree of water resistance, which roughly translates to the following (1 metre = 3.281 feet):[35]
Main Article ISO 6425
Water resistance rating Suitability Remarks
Water Resistant or 30 m Suitable for everyday use. Splash/rain resistant. NOT suitable for swimming, snorkelling, water related work and fishing. NOT suitable for diving.
Water Resistant 50 m Suitable for swimming, white water rafting, non-snorkeling water related work, and fishing. NOT suitable for diving.
Water Resistant 100 m Suitable for recreational surfing, swimming, snorkeling, sailing and water sports. not suitable for diving. This is the standard for children's digital watches.
Water Resistant 200 m Suitable for professional marine activity and serious surface water sports. suitable for diving.
Diver's 100 m Minimum ISO standard for scuba diving at depths not requiring helium gas. Diver's 100 m and 150 m watches are generally old(er) watches.
Diver's 200 m or 300 m Suitable for scuba diving at depths not requiring helium gas. Typical ratings for contemporary diver's watches.
Diver's 300+ m helium safe Suitable for saturation diving (helium enriched environment). Watches designed for helium mixed-gas diving will have additional markings to point this out.
Some watches use bar instead of meters, which may then be multiplied by 10, and then subtracted by 10. This is because 1 bar is equal to one atmosphere or 10 metres of water (therefore 1 bar at the surface and one more each 10 metres). to be approximately equal to the rating based on metres. Therefore, a 5 bar watch is equivalent to a 40 metre watch. Some watches are rated in atmospheres (atm), which are roughly equivalent to bar.
Monday, May 14, 2012
The Plastic History
A plastic material is any of a wide range of synthetic or semi-synthetic organicsolids that are moldable. Plastics are typically organic polymers of highmolecular mass, but they often contain other substances. They are usually synthetic, most commonly derived from petrochemicals, but many are partially natural.[1]
[edit]
Almost invariably, organic polymers mainly comprise plastics. The vast majority of these polymers are based on chains of carbon atoms alone or withoxygen, sulfur, or nitrogen as well. The backbone is that part of the chain on the main "path" linking a large number of repeat units together. To customize the properties of a plastic, different molecular groups "hang" from the backbone (usually they are "hung" as part of the monomers before linking monomers together to form the polymer chain). The structure of these "side chains" influence the properties of the polymer. This fine tuning of the properties of the polymer by repeating unit's molecular structure has allowed plastics to become an indispensable part of the twenty-first century world.Composition
[edit]Additives
Most plastics contain other organic or inorganic compounds blended in. The amount of additives ranges from zero percentage for polymers used to wrap foods to more than 50% for certain electronic applications. The average content of additives is 20% by weight of the polymer. Fillers improve performance and/or reduce production costs. Stabilizing additives include fire retardants to lower the flammability of the material. Many plastics contain fillers, relatively inert and inexpensive materials that make the product cheaper by weight. Typically fillers are mineral in origin, e.g., chalk. Some fillers are more chemically active and are called reinforcing agents. Since many organic polymers are too rigid for particular applications, they are blended with plasticizers, oily compounds that confer improvedrheology. Colourants are of course common additives, although their weight contribution is small. Many of the controversies associated with plastics are associated with the additives.[2]
[edit]Classification
Plastics are usually classified by their chemical structure of the polymer's backbone and side chains. Some important groups in these classifications are the acrylics, polyesters, silicones, polyurethanes, and halogenated plastics. Plastics can also be classified by the chemical process used in their synthesis, such as condensation, polyaddition, and cross-linking.[3]
[edit]Thermoplastics and thermosetting polymers
There are two types of plastics: thermoplastics and thermosetting polymers. Thermoplastics are the plastics that do not undergo chemical change in their composition when heated and can be moulded again and again. Examples include polyethylene,polypropylene, polystyrene, polyvinyl chloride, and polytetrafluoroethylene (PTFE).[4] Common thermoplastics range from 20,000 to 500,000 amu, while thermosets are assumed to have infinite molecular weight. These chains are made up of many repeating molecular units, known as repeat units, derived from monomers; each polymer chain will have several thousand repeating units.
Thermosets can melt and take shape once; after they have solidified, they stay solid. In the thermosetting process, a chemical reaction occurs that is irreversible. The vulcanization of rubber is a thermosetting process. Before heating with sulfur, the polyisoprene is a tacky, slightly runny material, but after vulcanization the product is rigid and non-tacky.
[edit]Other classifications
Other classifications are based on qualities that are relevant for manufacturing or product design. Examples of such classes are the thermoplastic and thermoset, elastomer, structural, biodegradable, and electrically conductive. Plastics can also be classified by various physical properties, such as density, tensile strength, glass transition temperature, and resistance to various chemical products.
[edit]Biodegradability
Main article: Biodegradable plastic
Biodegradable plastics break down (degrade) upon exposure to sunlight (e.g., ultra-violet radiation), water or dampness, bacteria, enzymes, wind abrasion, and in some instances rodent pest or insect attack are also included as forms of biodegradation orenvironmental degradation. Some modes of degradation require that the plastic be exposed at the surface, whereas other modes will only be effective if certain conditions exist in landfill or composting systems. Starch powder has been mixed with plastic as a filler to allow it to degrade more easily, but it still does not lead to complete breakdown of the plastic. Some researchers have actuallygenetically engineered bacteria that synthesize a completely biodegradable plastic, but this material, such as Biopol, is expensive at present.[5] The German chemical company BASF makes Ecoflex, a fully biodegradable polyester for food packaging applications.
[edit]Natural vs synthetic
Main article: Bioplastic
Most plastics are produced from petrochemicals. Motivated by the finiteness of petrochemical reserves and possibility of global warming, bioplastics are being developed. Bioplastics are made substantially from renewable plant materials such as cellulose and starch.[6]
In comparison to the global consumption of all flexible packaging, estimated at 12.3 million tonnes, estimates put global production capacity at 327,000 tonnes for related bio-derived materials.[7][8]
[edit]Crystalline vs amorphous
Some plastics are partially crystalline and partially amorphous in molecular structure, giving them both a melting point (the temperature at which the attractive intermolecular forces are overcome) and one or more glass transitions (temperatures above which the extent of localized molecular flexibility is substantially increased). The so-called semi-crystalline plastics include polyethylene, polypropylene, poly (vinyl chloride), polyamides (nylons), polyesters and some polyurethanes. Many plastics are completely amorphous, such as polystyrene and its copolymers, poly (methyl methacrylate), and all thermosets.
[edit]History
Early plastics were bio-derived materials such as egg and blood proteins, which are organic polymers. Treated cattle horns were used as windows for lanterns in the Middle Ages. Materials that mimicked the properties of horns were developed by treating milk-proteins (casein) with lye. In the 1800s the development of plastics accelerated with Charles Goodyear's discovery of vulcanization as a route to thermoset materials derived from natural rubber. Many storied materials were reported as industrial chemistry was developed in the 1800s. In the early 1900s, Bakelite, the first fully synthetic thermoset was reported by Belgian chemist Leo Baekeland. After the First World War, improvements in chemical technology led to an explosion in new forms of plastics. Among the earliest examples in the wave of new polymers were polystyrene (PS) and polyvinyl chloride (PVC). The development of plastics has come from the use of natural plastic materials (e.g., chewing gum, shellac) to the use of chemically modified natural materials (e.g., rubber, nitrocellulose, collagen, galalite) and finally to completely synthetic molecules (e.g., bakelite, epoxy, polyvinyl chloride).
[edit]Parkesine
The plastic material, parkesine, was patented by Alexander Parkes, In Birmingham, UK in 1856.[9] It was unveiled at the 1862 Great International Exhibition in London.[10] Parkesine won a bronze medal at the 1862 World's fair in London. Parkesine was made from cellulose (the major component of plant cell walls) treated with nitric acid as a solvent. The output of the process (commonly known as cellulose nitrate or pyroxilin) could be dissolved in alcohol and hardened into a transparent and elastic material that could be molded when heated.[11] By incorporating pigments into the product, it could be made to resemble ivory.
[edit]Bakelite
Main article: Bakelite
The first so called plastic based on a synthetic polymer was made from phenol and formaldehyde, with the first viable and cheap synthesis methods invented in 1907, by Leo Hendrik Baekeland, a Belgian-born American living in New York state. Baekeland was looking for an insulating shellac to coat wires in electric motors and generators. He found that combining phenol (C6H5OH) and formaldehyde (HCOH) formed a sticky mass and later found that the material could be mixed with wood flour, asbestos, or slate dust to create strong and fire resistant "composite" materials. The new material tended to foam during synthesis, requiring that Baekeland build pressure vessels to force out the bubbles and provide a smooth, uniform product, as he announced in 1909, in a meeting of the American Chemical Society.[12] Bakelite was originally used for electrical and mechanical parts, coming into widespread use in consumer goods in the 1920s. Bakelite was a purely synthetic material, not derived from living matter. It was also an early thermosetting plastic.
[edit]Representative polymers
[edit]Polystyrene
Main articles: Polystyrene and PVC
Polystyrene is a rigid, brittle, inexpensive plastic that has been used to make plastic modelkits and similar knick-knacks. It would also be the basis for one of the most popular "foamed" plastics, under the name styrene foam or Styrofoam. Foam plastics can be synthesized in an "open cell" form, in which the foam bubbles are interconnected, as in an absorbent sponge, and "closed cell", in which all the bubbles are distinct, like tiny balloons, as in gas-filled foam insulation and flotation devices. In the late 1950s, high impact styrene was introduced, which was not brittle. It finds much current use as the substance of toy figurines and novelties.
[edit]Polyvinyl chloride
Polyvinyl chloride (PVC, commonly called "vinyl")[13] incorporates chlorine atoms. The C-Cl bonds in the backbone are hydrophobic and resist oxidation (and burning). PVC is stiff, strong, heat and weather resistant, properties that recommend its use in devices for plumbing, gutters, house siding, enclosures for computers and other electronics gear. PVC can also be softened with chemical processing, and in this form it is now used for shrink-wrap, food packaging, and rain gear.
All PVC polymers are degraded by heat and light. When this happens, hydrogen chloride is released into the atmosphere and oxidation of the compound occurs.[14] Because hydrogen chloride readily combines with water vapor in the air to form hydrochloric acid,[15] polyvinyl chloride is not recommended for long-term archival storage of silver, photographic film or paper (mylar is preferable).[16]
[edit]Nylon
Main article: Nylon
The plastics industry was revolutionized in the 1930s with the announcement of polyamide (PA), far better known by its trade namenylon. Nylon was the first purely synthetic fiber, introduced by DuPont Corporation at the 1939 World's Fair in New York City.
In 1927, DuPont had begun a secret development project designated Fiber66, under the direction of Harvard chemist Wallace Carothersand chemistry department director Elmer Keiser Bolton. Carothers had been hired to perform pure research, and he worked to understand the new materials' molecular structure and physical properties. He took some of the first steps in the molecular design of the materials.
His work led to the discovery of synthetic nylon fiber, which was very strong but also very flexible. The first application was for bristles for toothbrushes. However, Du Pont's real target was silk, particularly silk stockings. Carothers and his team synthesized a number of different polyamides including polyamide 6.6 and 4.6, as well as polyesters.[17]
It took DuPont twelve years and US$27 million to refine nylon, and to synthesize and develop the industrial processes for bulk manufacture. With such a major investment, it was no surprise that Du Pont spared little expense to promote nylon after its introduction, creating a public sensation, or "nylon mania".
Nylon mania came to an abrupt stop at the end of 1941 when the USA entered World War II. The production capacity that had been built up to produce nylon stockings, or just nylons, for American women was taken over to manufacture vast numbers of parachutes for fliers and paratroopers. After the war ended, DuPont went back to selling nylon to the public, engaging in another promotional campaign in 1946 that resulted in an even bigger craze, triggering the so called nylon riots.
Subsequently polyamides 6, 10, 11, and 12 have been developed based on monomers which are ring compounds; e.g. caprolactam. Nylon 66 is a material manufactured by condensation polymerization.
Nylons still remain important plastics, and not just for use in fabrics. In its bulk form it is very wear resistant, particularly if oil-impregnated, and so is used to build gears, plain bearings, and because of good heat-resistance, increasingly for under-the-hood applications in cars, and other mechanical parts.
[edit]Rubber
Natural rubber is an elastomer (an elastic hydrocarbon polymer) that was originally derived from latex, a milky colloidal suspensionfound in the sap of some plants. It is useful directly in this form (indeed, the first appearance of rubber in Europe was cloth waterproofed with unvulcanized latex from Brazil) but, later, in 1839, Charles Goodyear invented vulcanized rubber; this a form of natural rubber heated with, mostly, sulfur forming cross-links between polymer chains (vulcanization), improving elasticity and durability.
[edit]Synthetic rubber
Main article: Synthetic rubber
The first fully synthetic rubber was synthesized by Sergei Lebedev in 1910. In World War II, supply blockades of natural rubber fromSouth East Asia caused a boom in development of synthetic rubber, notably styrene-butadiene rubber. In 1941, annual production of synthetic rubber in the U.S. was only 231 tonnes which increased to 840,000 tonnes in 1945. In the space race and nuclear arms race,Caltech researchers experimented with using synthetic rubbers for solid fuel for rockets. Ultimately, all large military rockets and missiles would use synthetic rubber based solid fuels, and they would also play a significant part in the civilian space effort.
[edit]Properties of plastics
The properties of plastics is defined chiefly by the organic chemistry of the polymer. such as hardness, density, and resistance to heat, organic solvents, oxidation, and ionizing radiation. In particular, most plastics will melt upon heating to a few hundred degreescelsius.[18] While plastics can be made electrically conductive, with the conductivity of up to 80 kS/cm in stretch-orientedpolyacetylene,[19] they are still no match for most metals like copper which have conductivities of several hundreds kS/cm.
[edit]Toxicity
Due to their insolubility in water and relative chemical inertness, pure plastics generally have low toxicity. Some plastic products contain a variety of additives, some of which can be toxic. For example, plasticizers like adipates and phthalates are often added to brittle plastics like polyvinyl chloride to make them pliable enough for use in food packaging, toys, and many other items. Traces of these compounds can leach out of the product. Owing to concerns over the effects of such leachates, the European Union has restricted the use of DEHP (di-2-ethylhexyl phthalate)and other phthalates in some applications. Some compounds leaching from polystyrene food containers have been proposed to interfere with hormone functions and are suspected human carcinogens.[20]
Whereas the finished plastic may be non-toxic, the monomers used in the manufacture of the parent polymers may be toxic. In some cases, small amounts of those chemicals can remain trapped in the product unless suitable processing is employed. For example, theWorld Health Organization's International Agency for Research on Cancer (IARC) has recognized that vinyl chloride, the precursor to PVC, as a human carcinogen.[20]
[edit]BPA controversy
Some polymers may also decompose into the monomers or other toxic substances when heated. In 2011, it was reported that "almost all plastic products" sampled released chemicals with estrogenic activity, although the researchers identified plastics which did not leach chemicals with estrogenic activity.[21]
The primary building block of polycarbonates, bisphenol A (BPA), is an estrogen-like endocrine disruptor that may leach into food.[20]Research in Environmental Health Perspectives finds that BPA leached from the lining of tin cans, dental sealants and polycarbonate bottles can increase body weight of lab animals' offspring.[22] A more recent animal study suggests that even low-level exposure to BPA results in insulin resistance, which can lead to inflammation and heart disease.[23]
As of January 2010, the LA Times newspaper reports that the United States FDA is spending $30 million to investigate indications of BPA being linked to cancer.[24]
Bis(2-ethylhexyl) adipate, present in plastic wrap based on PVC, is also of concern, as are the volatile organic compounds present innew car smell.
The European Union has a permanent ban on the use of phthalates in toys. In 2009, the United States government banned certain types of phthalates commonly used in plastic.[25]
[edit]Environmental issues
Further information: Marine debris and Great Pacific Garbage Patch
Plastics are durable and degrade very slowly; the chemical bonds that make plastic so durable make it equally resistant to natural processes of degradation. Since the 1950s, one billion tons of plastic have been discarded and may persist for hundreds or even thousands of years.[26] Perhaps the biggest environmental threat from plastic comes from nurdles,[27] which are the raw material from which all plastics are made. They are tiny pre-plastic pellets that kill large numbers of fish and birds that mistake them for food.
Prior to the ban on the use of CFCs in extrusion of polystyrene (and general use, except in life-critical fire suppression systems; seeMontreal Protocol), the production of polystyrene contributed to the depletion of the ozone layer; however, non-CFCs are currently used in the extrusion process.
[edit]Incineration of plastics
Plastic can be converted as a fuel since they are usually hydrocarbon-based and can be broken down into liquid hydrocarbon. One kilogram of waste plastic produces a liter of hydrocarbon.[28] In some cases, burning plastic can release toxic fumes. Burning the plastic polyvinyl chloride (PVC) may create dioxin.[29]
[edit]Recycling
Thermoplastics can be remelted and reused, and thermoset plastics can be ground up and used as filler, although the purity of the material tends to degrade with each reuse cycle. There are methods by which plastics can be broken back down to a feedstock state.
The greatest challenge to the recycling of plastics is the difficulty of automating the sorting of plastic wastes, making it labor intensive. Typically, workers sort the plastic by looking at the resin identification code, although common containers like soda bottles can be sorted from memory. Typically, the caps for PETE bottles are made from a different kind of plastic which is not recyclable, which presents additional problems to the automated sorting process. Other recyclable materials such as metals are easier to process mechanically. However, new processes of mechanical sorting are being developed to increase capacity and efficiency of plastic recycling.
While containers are usually made from a single type and color of plastic, making them relatively easy to be sorted, a consumer product like a cellular phone may have many small parts consisting of over a dozen different types and colors of plastics. In such cases, the resources it would take to separate the plastics far exceed their value and the item is discarded. However, developments are taking place in the field of active disassembly, which may result in more consumer product components being re-used or recycled. Recycling certain types of plastics can be unprofitable, as well. For example, polystyrene is rarely recycled because it is usually not cost effective. These unrecycled wastes are typically disposed of in landfills, incinerated or used to produce electricity at waste-to-energy plants.
A first success in recycling of plastics is Vinyloop, a recycling process and an approach of the industry to separate PVC from other materials through a process of dissolution, filtration and separation of contaminations. A solvent is used in a closed loop to elute PVC from the waste. This makes it possible to recycle composite structure PVC waste which normally is being incinerated or put in a landfill. Vinyloop-based recycled PVC's primary energy demand is 46 percent lower than conventional produced PVC. The global warming potential is 39 percent lower. This is why the use of recycled material leads to a significant better ecological footprint.[30]
In 1988, to assist recycling of disposable items, the Plastic Bottle Institute of the Society of the Plastics Industry devised a now-familiar scheme to mark plastic bottles by plastic type. A plastic container using this scheme is marked with a triangle of three "chasing arrows", which encloses a number giving the plastic type:
Plastics type marks: the resin identification code[31]
- PET (PETE), polyethylene terephthalate
- HDPE, high-density polyethylene
- PVC, polyvinyl chloride
- LDPE, low-density polyethylene,
- PP, polypropylene
- PS, polystyrene
- Other types of plastics (see list, below)
[edit]Common plastics and uses
Due to their relatively low cost, ease of manufacture, versatility, and imperviousness to water, plastics are used in an enormous and expanding range of products, from paper clips to spaceships. They have already displaced many traditional materials, such as wood,stone, horn and bone, leather, paper, metal, glass, and ceramic, in most of their former uses.
- Polyester (PES) – Fibers, textiles.
- Polyethylene terephthalate (PET) – Carbonated drinks bottles, peanut butter jars, plastic film, microwavable packaging.
- Polyethylene (PE) – Wide range of inexpensive uses including supermarket bags, plastic bottles.
- High-density polyethylene (HDPE) – Detergent bottles, milk jugs, and molded plastic cases.[32]
- Polyvinyl chloride (PVC) – Plumbing pipes and guttering, shower curtains, window frames, flooring.
- Polyvinylidene chloride (PVDC) (Saran) – Food packaging.
- Low-density polyethylene (LDPE) – Outdoor furniture, siding, floor tiles, shower curtains, clamshell packaging.
- Polypropylene (PP) – Bottle caps, drinking straws, yogurt containers, appliances, car fenders (bumpers), plastic pressure pipe systems.
- Polystyrene (PS) – Packaging foam/"peanuts", food containers, plastic tableware, disposable cups, plates, cutlery, CD and cassette boxes.
- High impact polystyrene (HIPS) -: Refrigerator liners, food packaging, vending cups.
- Polyamides (PA) (Nylons) – Fibers, toothbrush bristles, fishing line, under-the-hood car engine moldings.
- Acrylonitrile butadiene styrene (ABS) – Electronic equipment cases (e.g., computer monitors, printers, keyboards), drainage pipe.
- Polycarbonate (PC) – Compact discs, eyeglasses, riot shields, security windows, traffic lights, lenses.
- Polycarbonate/Acrylonitrile Butadiene Styrene (PC/ABS) – A blend of PC and ABS that creates a stronger plastic. Used in car interior and exterior parts, and mobile phone bodies.
- Polyurethanes (PU) – Cushioning foams, thermal insulation foams, surface coatings, printing rollers (Currently 6th or 7th most commonly used plastic material, for instance the most commonly used plastic found in cars).
[edit]Special purpose plastics
- Melamine formaldehyde (MF) – One of the aminoplasts, and used as a multi-colorable alternative to phenolics, for instance in moldings (e.g., break-resistance alternatives to ceramic cups, plates and bowls for children) and the decorated top surface layer of the paper laminates (e.g., Formica).
- Plastarch material – Biodegradable and heat resistant, thermoplastic composed of modified corn starch.
- Phenolics (PF) or (phenol formaldehydes) – High modulus, relatively heat resistant, and excellent fire resistant polymer. Used for insulating parts in electrical fixtures, paper laminated products (e.g., Formica), thermally insulation foams. It is a thermosetting plastic, with the familiar trade name Bakelite, that can be molded by heat and pressure when mixed with a filler-like wood flour or can be cast in its unfilled liquid form or cast as foam (e.g., Oasis). Problems include the probability of moldings naturally being dark colors (red, green, brown), and as thermoset it is difficult to recycle.
- Polyetheretherketone (PEEK) – Strong, chemical- and heat-resistant thermoplastic, biocompatibility allows for use in medical implant applications, aerospace moldings. One of the most expensive commercial polymers.
- Polyetherimide (PEI) (Ultem) – A high temperature, chemically stable polymer that does not crystallize.
- Polylactic acid (PLA) – A biodegradable, thermoplastic found converted into a variety of aliphatic polyesters derived from lactic acidwhich in turn can be made by fermentation of various agricultural products such as corn starch, once made from dairy products.
- Polymethyl methacrylate (PMMA) – Contact lenses, glazing (best known in this form by its various trade names around the world; e.g., Perspex, Oroglas, Plexiglas), aglets, fluorescent light diffusers, rear light covers for vehicles. It forms the basis of artistic and commercial acrylic paints when suspended in water with the use of other agents.
- Polytetrafluoroethylene (PTFE) – Heat-resistant, low-friction coatings, used in things like non-stick surfaces for frying pans, plumber's tape and water slides. It is more commonly known as Teflon.
- Urea-formaldehyde (UF) – One of the aminoplasts and used as a multi-colorable alternative to phenolics. Used as a wood adhesive (for plywood, chipboard, hardboard) and electrical switch housings.
[edit]Material properties of some thermoplastics
| name | Symbol | Density [g/cm3] | Tensile strength [MPa] | Flexural strength [MPa] | Elastic modulus [GPa] | Elongation at rupture [%] | Thermal stability [°C] | Expansion at 20°C [10−6/°C] | |
|---|---|---|---|---|---|---|---|---|---|
| High DensityPolyethylene | HDPE | 0.95 | 31 | 40 | 1.86 | 100 | 120 | 126 | [33] |
| Low DensityPolyethylene | LDPE | 0.92 | 17 | 14 | 0.29 | 500 | 90 | 160 | |
| Polyvinyl Chloride | PVC | 1.44 | 47 | 91 | 3.32 | 60 | 80 | 75 | |
| Polypropylene | PP | 0.91 | 37 | 49 | 1.36 | 350 | 150 | 90 | |
| Polyethylene terephthalate | PET | 1.35 | 61 | 105 | 1.35 | 170 | 120 | 70 | |
| Polymethylmethacrylate | PMMA | 1.19 | 61 | 103 | 2.77 | 4 | 100 | 65 | |
| Polycarbonate | PC | 1.2 | 68 | 95 | 2.3 | 130 | 120 | 66 | |
| Acrylonitrile butadiene styrene | ABS | 1.05 | 45 | 70 | 2.45 | 33 | 70 | 90 | |
| Polyamide | Nylon 6 | 1.13 | 60 | 91 | 2.95 | 60 | 110 | 66 | |
| Polyimide | PI | 1.38 | 96 | 143 | 3.1 | 7 | 380 | 43 | |
| Polysulfone | PSF | 1.25 | 68 | 115 | 2.61 | 75 | 160 | 56 | |
| Polyamide-imide, electrical grade | PAI | 1.41 | 138 | 193 | 4.1 | 12 | 260 | 30 | |
| Polyamide-imide, bearing grade | PAI | 1.46 | 103 | 159 | 5.5 | 6 | 260 | 25 | |
| Polytetrafluoroethylene | PTFE | 2.17 | 24 | 33 | 0.49 | 300 | 260 | 95 | |
| Polyetherimide | PEI | 1.27 | 105 | 151 | 2.9 | 60 | 210 | 31 | [34] |
| Polyether ether ketone | PEEK | 1.32 | 100 | 3.6 | 50 | 343 | |||
| Polyaryletherketone(strong) | PEAK | 1.46 | 136 | 213 | 12.4 | 2.1 | 267 | ||
| Polyaryletherketone(tough) | PEAK | 1.29 | 87 | 124 | 3 | 40 | 190 | ||
| Self-reinforcedpolyphenylene | SRP | 1.19 | 152 | 234 | 5.52 | 10 | 151 | ||
| Polyamide-imide | PAI | 1.42 | 152 | 241 | 4.9 | 15 | 278 |
NOTE: Bulk properties of pure cast or hot formed materials. Properties could change considerably by mechanical treatment and cold forming. Fiber and foils are not considered.
[edit]Etymology
The word plastic is derived from the Greek πλαστικός (plastikos) meaning capable of being shaped or molded, from πλαστός (plastos) meaning molded.[35][36] It refers to their malleability, or plasticity during manufacture, that allows them to be cast, pressed, or extrudedinto a variety of shapes—such as films, fibers, plates, tubes, bottles, boxes, and much more.
The common word plastic should not be confused with the technical adjective plastic, which is applied to any material which undergoes a permanent change of shape (plastic deformation) when strained beyond a certain point. Aluminum which is stamped or forged, for instance, exhibits plasticity in this sense, but is not plastic in the common sense; in contrast, in their finished forms, some plastics will break before deforming and therefore are not plastic in the technical sense.
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